examples/src/main/java/org/apache/spark/examples/ml/JavaNGramExample.java
/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.spark.examples.ml;

import org.apache.spark.sql.Dataset;
import org.apache.spark.sql.SparkSession;

// $example on$
import java.util.Arrays;
import java.util.List;

import org.apache.spark.ml.feature.NGram;
import org.apache.spark.sql.Row;
import org.apache.spark.sql.RowFactory;
import org.apache.spark.sql.types.DataTypes;
import org.apache.spark.sql.types.Metadata;
import org.apache.spark.sql.types.StructField;
import org.apache.spark.sql.types.StructType;
// $example off$

public class JavaNGramExample {
  public static void main(String[] args) {
    SparkSession spark = SparkSession
      .builder()
      .appName("JavaNGramExample")
      .getOrCreate();

    // $example on$
    List<Row> data = Arrays.asList(
      RowFactory.create(0, Arrays.asList("Hi", "I", "heard", "about", "Spark")),
      RowFactory.create(1, Arrays.asList("I", "wish", "Java", "could", "use", "case", "classes")),
      RowFactory.create(2, Arrays.asList("Logistic", "regression", "models", "are", "neat"))
    );

    StructType schema = new StructType(new StructField[]{
      new StructField("id", DataTypes.IntegerType, false, Metadata.empty()),
      new StructField(
        "words", DataTypes.createArrayType(DataTypes.StringType), false, Metadata.empty())
    });

    Dataset<Row> wordDataFrame = spark.createDataFrame(data, schema);

    NGram ngramTransformer = new NGram().setN(2).setInputCol("words").setOutputCol("ngrams");

    Dataset<Row> ngramDataFrame = ngramTransformer.transform(wordDataFrame);
    ngramDataFrame.select("ngrams").show(false);
    // $example off$

    spark.stop();
  }
}
